In addition to classical radiography systems in which a radiographic image of a patient is recorded on film, computed radiography systems and digital radiography systems are nowadays commonly used.
Computed radiography systems are for example systems that are based on storage phosphor technology.
Digital radiography systems are systems in which a radiation image is recorded on a flat panel detector such as a CMOS, a selenium detector, or the like.
In systems in which imaging is obtained by irradiation of a patient, an animal, or an object with high energy radiation, it is important that the image and the meta-data giving information pertaining to the image are linked.
Meta-data are all kinds of data to be associated with the image such as demographic data (patient name, gender, date of birth, etc.) and data relating to the exposure such as the product of the current through the x-ray tube (mA) and the time the tube was energized (s) milliampere-second (mAs), kiloVolts (kV), exposure type, exposure view. etc.
For example in a computed radiography system in which a radiographic image of a patient is recorded on a photostimulatable phosphor screen, which is conveyed in a cassette, the meta-data are entered in a workstation or retrieved from a hospital information system or a radiology information system and transferred onto an identification device which is coupled to the cassette. Meta-data can be written into a non-volatile device for example an EEPROM device which is provided on the cassette conveying the exposed phosphor screen, or the data can be transferred through radio-frequency transmission onto a radio-frequency tag provided on the cassette or on the screen.
The identified cassette conveying an exposed photo-stimulatable phosphor screen is then fed into a read out apparatus (also referred to as a ‘digitizer’) where the meta-data are read from the identification device and where the radiographic image, which is stored in the phosphor screen, is read out. The radiographic image is read out by scanning the exposed photo-stimulatable phosphor screen with stimulating radiation and by converting the image-wise modulated light which is emitted by the screen upon stimulation into a digital signal representation of the radiographic image.